1. Field of the Invention
The present invention relates to a radiation measuring apparatus which is designed so as to transmit detected signals obtained from a radiation detector using an optical fiber.
2. Description of the Prior Art
FIG. 1 is a block diagram showing a conventional radiation measuring apparatus. In FIG. 1, reference numeral 1 is a radiation detector which outputs a detected pulse signal having a pulse height in accordance with the detected radiation energy, 2 an amplifier which amplifies the detected pulse signal obtained from the radiation detector 1, 3 an electro-optical converter such as a light emitting diode or a laser diode which converts the detected pulse signal amplified by the amplifier 2 into an optical signal, 4 an optical fiber which transmits the optical signal obtained from the electro-optical converter 3, 5 an opto-electrical converter such as a photo diode which converts the optical signal transmitted through the optical fiber 4 into an electrical signal, 6 an amplifier which amplifies the detected pulse signal obtained from the opto-electrical converter 5, and 7 an output terminal from which the detected pulse signal amplified by the amplifier 6 is output.
Next, the operation will be described. The radiation detector 1 detects radiation and outputs a detected pulse signal. The detected pulse signal has a fixed polarity, and its pulse height is proportional to the energy of the detected radiation. The frequency of generation of the detected pulse signal is proportional to intensity of the detected radiation. After being amplified by the amplifier 2, the detected pulse signal is converted into an optical pulse signal by the electro-optical converter 3. After being transmitted through the optical fiber 4, the optical pulse signal is converted back into an electric pulse signal by the opto-electrical converter 5, and further amplified by the amplifier 6 to be supplied to the output terminal 7. The detected pulse signal obtained from the output terminal 7 is sent to a counter circuit or a pulse height analyzer provided in the following stage though not shown, and used for measurement of intensity of detected radiation or distribution of energy and the like.
Since a conventional radiation measuring apparatus is constituted as described above, the transmission loss of the optical fiber 4 is subject to change with the passage of time and consequently, sometimes the pulse height of the detected pulse signal obtained at the output terminal 7 varies as a result thereof. This has been a very important problem from the viewpoint of measuring energy of detected radiation based on the pulse height of the detected pulse signal.